install a new hdd in the g5??

i dont know much about macs, ive learned fast since we got out g5, but i havent figured out this, how do i install a new hdd in the g5? i know that 160gb hdd is big, but if i ever do need to install a new one how would i? the power and data connecters are not what i im custom too. the power cord has only 2 wires, and the data has 4 i think. there is one slot open, and a power and data cable hanging lose ready for a new one.